Image reproduction systems provide a means to reproduce images in a variety of formats. An example of an image reproduction system is a xerographic (“dry writing”) system. In this system, a latent image of electrical charges is formed on a photosensitive film. The location of the electrical charge forming the latent image is usually optically controlled. More specifically, in a digital xerographic system, the formation of the latent image is controlled by a raster output scanning device, usually a laser or LED source.
Although a xerographic system usually produces a faithful reproduction of the original image, defects in the subsystems of the xerographic may give rise to visible streaks in the reproduced image. Streaks are primarily one-dimensional defects in an image that run parallel to the process or slow-scan direction.
Streaks are caused by “non-ideal” responses of xerographic components in the marking engine. For example, these streaks may be caused by contamination of a wire module in a hybrid scavengeless development subsystem, contamination of a charging device or grid, scratches in the photoreceptor, differential abrasions of the photoreceptor, and raster output scanning device spot-size or intensity variations.
In a uniform patch of gray, streaks may appear as a variation in the gray level. In general, “gray” refers to the intensity value of any single color separation layer, whether the toner is black, cyan, magenta, yellow, or some other color.
Another frequent source of streaks is the non-uniformity of the raster output scanning device itself. This non-uniformity occurs because of problems in meeting the tight requirements of the manufacturing process and decreases the yield of raster output scanning device's meeting specifications.
As shown in FIG. 1, a measured L* profile in the fast-scan direction decreases in L* on the left and right side of the print, mainly due to the non-uniformity of the raster output scanning device. The dotted line 1 in FIG. 1 represents the desired measured L* or uniformity. The solid line 2 represents the actual measured L*. In this instance, the measured L* has non-uniformities which are the source of streaks in the rendered image.
In a color xerographic machine, this undesirable response of line 2 of FIG. 1 may cause visible color non-uniformities. The visible color non-uniformities are low spatial frequency streaks in the separations that although unobjectionable for a single color separation, may cause an undesirable color shift for overlaid colors.
Color uniformity requirements are usually tough to meet, and traditional solution approaches, as is noted below, rely on expensive parts or subsystems that meet tight allocations.
Most of the existing methods to mitigate streaks are “passive;” i.e., the methods require using subsystem components of high quality with tight latitudes over the critical parameters. For example, the requirement could be a softer toner with low abrasion, a better coating for the hybrid scavengeless developer wire, a more accurate optical system for the raster output scanning device, etc.
As a result of these passive approaches, manufacturing and maintenance costs for xerographic products increase dramatically in order to cope with more stringent image quality requirements. In addition, the reliability decreases as these subsystem components fail over time.
Therefore, it is desirable to provide a system and/or method that mitigate the streaks parallel to the process direction without using subsystem components of high quality with tight latitudes over the critical parameters. Moreover, it is desirable to provide a system and/or method that mitigate the streaks parallel to the process direction without increasing manufacturing or maintenance costs.
It is further desirable to provide a system and/or method that mitigate the streaks parallel to the process direction that utilizes the raster output scanning device as the actuator to compensate for streaks. It is also desirable to a system and/or method that mitigate the streaks parallel to the process direction that not only improves uniformity for a given halftone and/or area coverage, but improves the uniformity over a set of halftones and/or area coverages of interest.